Disazo dyes and inks containing them

ABSTRACT

Compounds of Formula (1) and salts thereof:                    
     wherein: 
     A is optionally substituted phenyl; 
     R 1  and R 2  are each independently optionally substituted alkyl or optionally substituted alkoxy; and 
     R 4  and R 5  are each independently H, optionally substituted alkyl or optionally substituted aryl; 
     provided that (i) at least one of R 1  and R 2  carries an —OH group; and 
     (ii) A is not of the formula:                    
      wherein m is 1, 2 or 3. 
     The compounds are useful as dyes for ink jet printing inks.

This application is the National Phase of International ApplicationPCT/GB00/00054 filed Jan. 11, 2000 which designated the U.S. and thatInternational Application was published under PCT Article 21(2) inEnglish.

This invention relates to compounds suitable for use as dyes, to inksand to their use in ink jet printing (“IJP”). IJP is a non-impactprinting technique in which droplets of ink are ejected through a finenozzle onto a substrate without bringing the nozzle into contact withthe substrate.

There are many demanding performance requirements for dyes and inks usedin IJP. For example they desirably provide sharp, non-feathered imageshaving good water-fastness, light-fastness and optical density. The inksare often required to dry quickly when applied to a substrate to preventsmudging, but they should not form a crust over the tip of an ink jetnozzle because this will stop the printer from working. The inks shouldalso be stable to storage over time without decomposing or forming aprecipitate which could block the fine nozzle.

According to the present invention there is provided a compound ofFormula (1) and salts thereof:

wherein:

A is optionally substituted phenyl;

R¹ and R² are each independently optionally substituted alkyl oroptionally substituted alkoxy; and

R⁴ and R⁵ are each independently H, optionally substituted alkyl oroptionally substituted aryl;

provided that (i) at least one of R¹ and R² carries an —OH group; and

(ii) A is not of the formula:

 wherein m is 1, 2 or 3.

Preferably A is phenyl carrying one or two substituents.

The optional substituents which may be present on A are preferablyselected from —OH; optionally substituted amino, especially —NH₂; halo,especially Cl, Br and F; ester, especially —CO₂—C₁-alkyl; —CN; —NO₂;optionally substituted alkyl; optionally substituted alkoxy; —CO₂H;—SO₃H; —SO₂NR³R³; —OR³; or —SR³; wherein each R³ independently is H or

C₁₋₄-alkyl. Especially preferred optional substituents for A areselected from optionally substituted C₁₋₄-alkyl and optionallysubstituted C₁₋₄-alkoxy, the preferred optional substituents beingselected from carboxylic acid, sulphonic acid and phosphoric acid.

R₁ and R² are preferably each independently optionally substitutedC₁₋₄-alkyl or C₁₋₄-alkoxy, more preferably optionally substitutedC₁₋₄-alkoxy, provided that at least one of R₁ and R² carries an —OHgroup. The optional substituents which may be present on R¹, R², R⁴ andR⁵ are preferably selected from —NH₂; halo, especially Cl, Br and F;ester, especially —CO₂—C₁₋₄-alkyl; —O—C₁₋₄-alkyl; —CO₂H; —SO₃H; —OR³; or—SR³; wherein each R³ independently is H or C1-4-alkyl, provided that atleast one of R¹ and R² carries an —OH group.

Preferably both R₁ and R² carry an —OH group.

Preferably R⁴ and R⁵ are each independently H, optionally substitutedC₁₋₄-alkyl or optionally substituted phenyl, more preferably H, orC₁₋₄-alkyl or phenyl carrying 1 or 2 groups selected from carboxy andsulpho. More preferably R⁴ and R⁵ are both H.

The compounds of Formula (1) may be prepared by diazotising a compoundof the Formula (2) to give a diazonium salt and coupling the resultantdiazonium salt with a 1-hydroxy-3,6-disulpho-7-aminonaphthalene:

wherein A, R¹ and R² are as hereinbefore defined.

The hydroxy group(s) on R¹ and/or R² may be protected during thediazotisation, for example using an acid labile or base labileprotecting group. The acetoxy protecting group is particularlyconvenient and inexpensive.

The diazotisation is preferably performed at a temperature below 6° C.,more preferably at a temperature in the range −10° C. to 5° C.Preferably the diazotisation is performed in water, preferably at a pHbelow 7. Dilute mineral acid, e.g. HCl or H₂SO₄, may be used to achievethe desired acidic conditions.

The compound of Formula (2) may be prepared by diazotising a compound offormula A—NH₂ and coupling onto an aniline compound carrying R¹ and R²groups at the 2- and 5- positions respectively, wherein A, R¹ and R² areas hereinbefore defined.

Preferred salts are alkali metal salts (especially lithium, sodium andpotassium salts), ammonium and substituted ammonium salts and mixturesthereof. Especially preferred salts are sodium, potassium and lithiumsalts, salts with ammonia and volatile amines and mixtures thereof. Thelithium salts have good solubility, forming particularly storage stableinks with low toxicity and low tendency to block ink jet nozzles.

The compounds may be converted into a desired salt using knowntechniques. For example, an alkali metal salt of a compound may beconverted into the ammonium or substituted ammonia salt by dissolving analkali metal salt of the compound in water, acidifying with a mineralacid and adjusting the pH of the solution to pH 9 to 9.5 with ammonia orthe amine and removing the alkali metal cations by dialysis or by use ofan ion exchange resin.

Examples of amines which may be used to form such salts includemethylamine, dimethylamine, trimethylamine, tetramethylamine,ethylamine, n-propylamine, iso-propylamine, n-butylamine,iso-butylamine, sec-butylamine, tert-butylamine, piperidine, pyridine,morpholine, allylamine, diethylamine, triethylamine and mixturesthereof. It is not essential that the dyes are completely in the form ofthe ammonium salt or substituted ammonium salt and mixed alkali metaland either ammonium salt or substituted ammonium salt are effective,especially those in which at least 50% of the cations are ammonium orsubstituted ammonium ions.

Still further salts are those with the counter ions described in U.S.Pat. No. 5,830,265, claim 1, integer (b), which are included herein byreference thereto.

The compounds of Formula (1) may exist in tautomeric forms other thanthose shown in this specification. These tautomers are included withinthe scope of the present claims.

According to a second aspect of the present invention there is providedan ink comprising a compound of Formula (1) or salt thereof and a liquidmedium or a low melting point solid medium.

A preferred ink comprises:

(a) from 0.01 to 30 parts of a compound of the Formula (1) or saltthereof; and

(b) from 70 to 99.99 parts of a liquid medium or a low melting pointsolid medium;

wherein all parts are by weight and the number of parts of (a)+(b)=100.

The number of parts of component (a) is preferably from 0.1 to 20, morepreferably from 0.5 to 15, and especially from 1 to 5 parts. The numberof parts of component (b) is preferably from 99.9 to 80, more preferablyfrom 99.5 to 85, especially from 99 to 95 parts.

When the medium is a liquid, preferably component (a) is completelydissolved in component (b). Preferably component (a) has a solubility incomponent (b) at 20° C. of at least 10%. This allows the preparation ofliquid dye concentrates which may be used as an ink or to prepare inksand reduces the chance of the dye precipitating if evaporation of theliquid medium occurs during storage.

Preferred liquid media include water, a mixture of water and an organicsolvent and an organic solvent free from water.

When the liquid medium comprises a mixture of water and an organicsolvent, the weight ratio of water to organic solvent is preferably from99:1 to 1:99, more preferably from 99:1 to 50:50 and especially from95:5 to 80:20.

It is preferred that the organic solvent present in the mixture of waterand organic solvent is a water-miscible organic solvent or a mixture ofsuch solvents. Preferred water-miscible organic solvents includeC₁₋₆-alkanols, preferably methanol, ethanol, n-propanol, isopropanol,n-butanol, sec-butanol, tert-butanol, n-pentanol, cyclopentanol andcyclohexanol; linear amides, preferably dimethylformamide ordimethylacetamide; ketones and ketone-alcohols, preferably acetone,methyl ether ketone, cyclohexanone and diacetone alcohol; water-miscibleethers, preferably tetrahydrofuran and dioxane; diols, preferably diolshaving from 2 to 12 carbon atoms, for example pentane-1,5-diol, ethyleneglycol, propylene glycol, butylene glycol, pentylene glycol, hexyleneglycol and thiodiglycol and oligo- and poly-alkyleneglycols, preferablydiethylene glycol, triethylene glycol, polyethylene glycol andpolypropylene glycol; triols, preferably glycerol and 1,2,6-hexanetriol;mono-C₁₋₄-alkyl ethers of diols, preferably mono-C₁₋₄-alkyl ethers ofdiols having 2 to 12 carbon atoms, especially 2-methoxyethanol,2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol,2-[2-(2-methoxyethoxy)ethoxy]ethanol,2-[2-(2-ethoxyethoxy)-ethoxy]-ethanol and ethyleneglycol monoallylether;cyclic amides, preferably 2-pyrrolidone, N-methyl-2-pyrrolidone,N-ethyl-2-pyrrolidone, caprolactam and 1,3-dimethylimidazolidone; cyclicesters, preferably caprolactone; sulphoxides, preferably dimethylsulphoxide and sulpholane. Preferably the liquid medium comprises waterand 2 or more, especially from 2 to 8, water-soluble organic solvents.

Especially preferred water-soluble organic solvents are cyclic amides,especially 2-pyrrolidone, N-methyl-pyrrolidone and N-ethyl-pyrrolidone;diols, especially 1,5pentane diol, ethyleneglycol, thiodiglycol,diethyleneglycol and triethyleneglycol; and mono- C₁₋₄-alkyl andC₁₋₄-alkyl ethers of diols, more preferably mono- C₁₋₄-alkyl ethers ofdiols having 2 to 12 carbon atoms, especially((2-methoxy)-2-ethoxy)-2-ethoxyethanol.

Examples of further suitable ink media comprising a mixture of water andone or more organic solvents are described in U.S. Pat. No. 4,963,189,U.S. Pat. No. 4,703,113, U.S. Pat. No. 4,626,284 and EP 4,251,50A.

When the liquid medium comprises an organic solvent free from water,(i.e. less than 1% water by weight) the solvent preferably has a boilingpoint of from 30° to 200° C., more preferably of from 40° to 150° C.,especially from 50 to 125° C. The organic solvent may bewater-immiscible, water-miscible or a mixture of such solvents.Preferred water-miscible organic solvents are any of the hereinbeforedescribed water-miscible organic solvents and mixtures thereof.Preferred water-immiscible solvents include, for example, aliphatichydrocarbons; esters, preferably ethyl acetate; chlorinatedhydrocarbons, preferably CH₂Cl₂; and ethers, preferably diethyl ether;and mixtures thereof.

When the liquid medium comprises a water-immiscible organic solvent,preferably a polar solvent is included because this enhances solubilityof the dye in the liquid medium. Examples of polar solvents includeC₁₋₄-alcohols. In view of the foregoing preferences it is especiallypreferred that where the liquid medium is an organic solvent free fromwater it comprises a ketone (especially methyl ethyl ketone) &/or analcohol (especially a C₁₋₄-alkanol, more especially ethanol orpropanol).

The organic solvent free from water may be a single organic solvent or amixture of two or more organic solvents. It is preferred that when themedium is an organic solvent free from water it is a mixture of 2 to 5different organic solvents. This allows a medium to be selected whichgives good control over the drying characteristics and storage stabilityof the ink.

Ink media comprising an organic solvent free from water are particularlyuseful where fast drying times are required and particularly whenprinting onto hydrophobic and non-absorbent substrates, for exampleplastics, metal and glass.

Preferred low melting solid media have a melting point in the range from60° C. to 125° C. Suitable low melting point solids include long chainfatty acids or alcohols, preferably those with C₁₈₋₂₄ chains, andsulphonamides. The compounds of Formula (1) may be dissolved in the lowmelting point solid or may be finely dispersed in it.

The compounds of the invention may be used as the sole colorant in inksbecause of their attractive black shade. However, if desired, one maycombine the dyes with one or more further colorants if a slightlydifferent shade is required for a particular end use. The furthercolorants are preferably dyes. When further colorants are included inthe ink these are preferably selected from black, cyan and yellowcolorants and combinations thereof.

Preferred black colorants include C.I.Food Black 2, C.I.Direct Black 19,C.I.Reactive Black 31, PRO-JET Fast Black 2, C.I.Direct Black 195;C.I.Direct Black 168; and black dyes described in patents by Lexmark(e.g. EP 0 539,178 A2, Example 1, 2, 3, 4 and 5), Orient Chemicals (e.g.EP 0 347 803 A2, pages 5-6, azo dyes 3, 4, 5, 6, 7, 8, 12, 13, 14, 15and 16) and Seiko Epson Corporation.

Preferred cyan colorants include C.I.Direct Blue 199; C.I.Acid Blue 9;C.I.Direct Blue 307; C.I.Reactive Blue 71; and C.I.Direct Blue 85.

Preferred yellow colorants include C.I.Direct Yellow 142; C.I.DirectYellow 132;

C.I.Direct Yellow 86; C.I.Direct Yellow 85; and C.I.Acid Yellow 23.

However, as mentioned above, it is not normally necessary to use furthercolorants in conjunction with dyes of the present invention.

The ink may also contain additional components conventionally used inink jet printing inks, for example viscosity and surface tensionmodifiers, corrosion inhibitors, biocides, kogation reducing additivesand surfactants which may be ionic or non-ionic.

A further aspect of the invention provides a process for printing animage on a substrate comprising applying an ink containing a compound ofFormula (1) to the substrate by means of an ink jet printer.

The ink used in this process is preferably as defined in the secondaspect of the present invention.

The ink jet printer preferably applies the ink to the substrate in theform of droplets which are ejected through a small orifice onto thesubstrate. Preferred ink jet printers are piezoelectric ink jet printersand thermal ink jet printers. In thermal ink jet printers, programmedpulses of heat are applied to the ink in a reservoir by means of aresistor adjacent to the orifice, thereby causing the ink to be ejectedin the form of small droplets directed towards the substrate duringrelative movement between the substrate and the orifice. Inpiezoelectric ink jet printers the oscillation of a small crystal causesejection of the ink from the orifice.

The substrate is preferably paper, plastic, a textile, metal or glass,more preferably paper, an overhead projector slide or a textilematerial, especially paper.

Preferred papers are plain or treated papers which may have an acid,alkaline or neutral character.

Preferred papers are plain or treated papers which may have an acid,alkaline or neutral character. Examples of commercially availabletreated papers include HP Premium Coated Paper (available from HewlettPackard Inc.), HP Photopaper (available from Hewlett Packard Inc.),Stylus Pro 720 dpi Coated Paper, Epson Photo Quality Glossy Film(available from Seiko Epson Corp.), Epson Photo Quality Glossy Paper(available from Seiko Epson Corp.), Canon HR 101 High Resolution Paper(available from Canon), Canon GP 201 Glossy Paper (available fromCanon), and Canon HG 101 and HG201 High Gloss Film (available fromCanon).

A further aspect of the present invention provides a paper, an overheadprojector slide or a textile material printed with an ink, a compound orby means of a printing process as hereinbefore defined.

A still further as aspect of the present invention provides an ink jetprinter cartridge, optionally refillable, containing an ink according tothe second aspect of the present invention.

The following examples illustrate how compounds according to theinvention may be synthesised.

The compounds and inks of the invention have attractive, neutral blackshades and are particularly well suited for the ink jet printing of textand images. The inks have good storage stability and low tendency toblock the very fine nozzles used in ink jet printers. Furthermore, theresultant images have good optical density, light-fastness, wet-fastnessand resistance to fading in the presence of oxidising air pollutants.

The invention is further illustrated by the following examples in whichall parts and percentages are by weight unless specified otherwise.

EXAMPLE 1

Preparation of

Step 1—Preparation of 4-Aminophenoxyacetic Acid

4-Acetylaminophenol (302 g) and sodium hydroxide (80 g) were dissolvedin water (1500 ml) and sodium chloroacetate (500 g) was added slowly,followed by sodium carbonate (200 g). After refluxing overnight and thencooling to room temperature the product was isolated by filtration. Thecrude product was purified by washing with acetone (3×3000 ml) to removeunreacted starting material. After drying at 50° C. the solid wasstirred in hydrochloric acid (4000 ml, 2M) at 70-80° C. until hydrolysiswas complete. After adjusting the pH to 4-5 with sodium hydroxide theprecipitated product was filtered- off and washed with acetone (2000ml). The yield of 4-aminophenoxyacetic acid was 262 g.

Step 2—Preparation of 1,4-di-(2-Acetoxyethoxy)hydroquinone

Hydroquinone bis-(2-hydroxyethyl)ether (179 g), acetic acid (1000 ml)and acetic anhydride (300 ml) were stirred and heated under refluxovernight. After cooling to room temperature and drowning into water (2l) the product was isolated by filtration, washed with water, dried andrecrystallised from ethanol to give 212 g of product.

Step 3—Preparation of 2-Nitro-1,4-di-(2-Acetoxyethyoxy)hydroquinone

The product of step 2 (211.5 g) was dissolved in acetic acid (1800 ml).A mixture of nitric acid (51.9 ml) and acetic acid (200 ml) was thenadded over 20 minutes keeping the temperature below 20° C. Afterstirring at room temperature overnight the solution was drowned intowater (9000 ml) and the product isolated by filtration, washed withwater and recrystallised from ethanol to give 209 g of product.

Step 4—Preparation of 2,5-di-(2-Acetoxyethoxy)aniline

The product of step 3 (115 g) was dissolved in ethanol at 50° C. andreduced with hydrogen in the presence of palladium catalyst (2 g, 5%Pd/C). When uptake of hydrogen ceased the solution was screened toremove the catalyst and the filtrates allowed to cool to roomtemperature. The crystalline solid was isolated by filtration and driedunder vacuum to give 90 g of product.

Step 5—Preparation of4-(4-Carboxymethoxyphenyl)azo-2.5-di-(2-Acetoxyethoxy)aniline

4-Aminophenoxyacetic acid (10.02 g) prepared as described in step 1 wasstirred in water (300 ml) and hydrochloric acid (20 ml). After coolingbelow 10° C., sodium nitrite (4.55 g) was added slowly. After stirringfor a further hour, excess nitrous acid was destroyed using sulphamicacid to give a diazonium salt solution.

2,5-di-(2-acetoxyethoxy)aniline (17.82 g) was dissolved in acetone (500ml) and added to the above diazonium salt solution. After stirringovernight at room temperature the precipitated product was filtered-off,washed with water and used without further purification.

Step 6—Preparation of the Title Product

The product of step 5 was dissolved in water by raising to pH9. Sodiumnitrite (8.28 g) was added and the mixture added to a mixture of water(100 ml) and hydrochloric acid (20 ml). After stirring for 1 hour atroom temperature excess nitrous acid was destroyed by sulphamic acid.

1-Hydroxy-3,6-disulpho-7-aminonaphthalene (16.2 g) was dissolved inwater (300 ml) and the pH raised to 10 by addition of sodium hydroxidesolution (2M). After cooling below 10° C., sodium carbonate (10 g) wasadded. The diazonium salt solution prepared as described in the previousparagraph was then added slowly, maintaining the pH at 10.5-11. Afterstirring for 1 hr, sodium hydroxide (120 g) was added and the solutionheated to 60-65° C. for 2 hrs. The pH was adjusted to 7 and ammoniumchloride (15% w/v) added to precipitate the dye which was isolated byfiltration at 70° C. The isolated solid was washed with hot ammoniumchloride solution (20% w/v) and pulled dry on the filter. Afterconversion to the free acid the black dye was re-dissolved in ammoniasolution and dialysed to low conductivity. The title product in the formof its ammonium salt was isolated by evaporating the water at 50° C.

EXAMPLE 2

Preparation of

Example 1 was repeated except that in place of 4-aminophenoxyacetic acidthere was used 2,5-disulphoaniline.

EXAMPLE 3

Preparation of

Example 1 was repeated except that in place of1,4-di-(2-acetoxyethoxy)hydroquinone there was used1,4-di(3-acetoxypropoxy)hydroquinone and in place of4-aminophenoxyacetic acid there was used 4-aminophenylacetic acid.

EXAMPLE 4

Preparation of

Example 1 was repeated except that in place of1,4-di-(2-acetoxyethoxy)hydroquinone there was used1,4-di-(3-acetoxypropoxy)hydroquinone.

EXAMPLE 5

Preparation of

Example 1 was repeated except that in place of1,4-di-(2-acetoxyethoxy)hydroquinone there was used1,4-di-(2,3-diacetoxypropoxy)hydroquinone.

EXAMPLE 6-15 Mixtures

The dye mixtures described in Table A may be prepared in which all partsare by weight and are shown in brackets. CID means C.I.Direct, CIR meansC.I.Reactive and CIA means C.I.Acid.

TABLE A Example 6 7 8 9 10 11 12 13 14 15 Dye from Example 1(80) 2(90)3(60) 4(75) 5(95) 1(92) 2(89) 3(81) 4(60) 5(77) No. CID Yellow 132 (10)(4) (7) CID Yellow 142 (10) (5) CID Yellow 86 (5) (6) CIA Yellow 23 (10)(10) CIA Blue 9 (5) CIA Blue 307 (8) CID Black 168 (11) CI Food Black 2(10) (20) CID Black 19 (30) (15) (20)

Inks

The inks described in Tables I and II may be prepared wherein the Dyedescribed in the first column is the Dye or mixture made in the aboveexample of the same number. Numbers quoted in the second column onwardsrefer to the number of parts of the relevant ingredient and all partsare by weight. The inks may be applied to paper by thermal or piezo inkjet printing.

The following abbreviations are used in Table I and II:

PG=propylene glycol

DEG=diethylene glycol

NMP=N-methyl pyrollidone

DMK=dimethylketone

IPA=isopropanol

MEOH=methanol

2P=2-pyrollidone

MIBK=methylisobutyl ketone

P12=propane-1,2-diol

BDL=butane-2,3-diol

CET=cetyl ammonium bromide

PHO=Na₂HPO₄ and

TBT=tertiary butanol

TDG=thiodiglycol

TABLE I Dye/ Dye/ Mixture Na Mixture Content Water PG DEG NMP DMK NaOHStearate IPA MEOH 2P MIBK 1 2.0 80 5 6 4 5 2 3.0 90 5 5 0.2 3 10.0 85 33 3 5 1 4 2.1 91 8 1 5 3.1 86 5 0.2 4 5 6 1.1 81 9 0.5 0.5 9 7 2.5 60 415 3 3 6 10 5 4 8 5 65 20 10 9 2.4 75 5 4 5 6 5 10 4.1 80 3 5 2 10 0.311 3.2 65 5 4 6 5 4 6 5 12 5.1 96 4 13 10.8 90 5 5 14 10.0 80 2 6 2 5 14 15 1.8 80 5 15 1 2.6 84 11 5 2 3.3 80 2 10 2 6 3 12.0 90 7 0.3 3 4 5.469 2 20 2 1 3 3 5 6.0 91 4 5

TABLE II Dye/ Dye/ Mixture Mixture Content Water PG DEG NMP CET TBT TDGBDL PHO 2P PI2 6 3.0 80 15 0.2 5 7 9.0 90 5 1.2 5 8 1.5 85 5 5 0.15 5.00.2 9 2.5 90 6 4 0.12 10 3.1 82 4 8 0.3 6 11 0.9 85 10 5 0.2 12 8.0 90 55 0.3 13 4.0 70 10 4 1 4 11 14 2.2 75 4 10 3 2 6 15 10.0 91 6 3 10 9.076 9 7 3.0 0.95 5 3 5.0 78 5 11 6 11 5.4 86 7 7 14 2.1 70 5 5 5 0.1 0.20.1 5 0.1 5 8 2.0 90 10 1 2 88 10 2 5 78 5 12 5 1 8 70 2 8 15 5 2 10 808 12 1 10 80 10

EXAMPLES 16-20

The method of Example 1 may be repeated except that in place of4-aminophenoxyacetic acid the intermediates described in the secondcolumn Table III may be used to give the compounds shown in the finalcolumn of Table III.

TABLE III Intermediate used in place of 4- Example aminophenoxyaceticacid in example 1 Product 16 2-amino-5-methyl benzoic acid

17 2-sulpho-4-methyl aniline

18 2-sulpho-4-methoxy aniline

19 2-carboxy-4,5-dimethoxy aniline

20 2-methyl-4-sulpho aniline

What is claimed is:
 1. A compound of Formula (1) or a salt thereof:

wherein: A is optionally substituted phenyl; R¹ and R² are eachindependently optionally substituted alkyl or optionally substitutedalkoxy; and R⁴ and R⁵ are each independently H, optionally substitutedalkyl or optionally substituted aryl; provided that (i) at least one ofR¹ and R² carries an —OH group; and (ii) A is not of the formula:

 wherein m is 1, 2or
 3. 2. A compound according to claim 1 wherein R⁴and R⁵ are H.
 3. A compound according to claim 1 or 2 wherein theoptional substituents which may be present on A are selected from —OH;optionally substituted amino; halo; ester; —CN; —NO₂; optionallysubstituted alkyl; optionally substituted alkoxy; —CO₂H; —SO₃H;—SO₂NR³R³; —OR³; or —SR³; wherein each R³ independently is H orC₁₋₄-alkyl.
 4. A compound according to any one of the preceding claimswherein R¹ and R² are each independently optionally substitutedC₁₋₄-alkyl or optionally substituted C₁₋₄-alkoxy, provided that at leastone of R¹ and R² carries an —OH group.
 5. A compound according to anyone of the preceding claims wherein both R¹ and R² carry an —OH group.6. A compound according to any one of the preceding claims wherein m is1 or 2; and one of R¹ and R² is —OC₁₋₄-alkyl—OH and the other is—OC₁₋₄-alkyl or —O—C₁₋₄-alkyl—OH.
 7. An ink comprising a compoundaccording to any one of the preceding claims and a liquid medium or alow melting point solid medium.
 8. An ink according to claim 7 whichcontains a further colorant selected from black, cyan and yellowcolorants.
 9. A process for printing an image on a substrate comprisingapplying an ink containing a compound according to any one of claims 1to 6 to the substrate by means of an ink jet printer.
 10. A paper, anoverhead projector slide or a textile material printed with an inkaccording to claim 7 or 8, a compound according to any one of claims 1to 6 or by means of a process according to claim
 9. 11. An ink jetprinter cartridge, optionally refillable, containing an ink according toclaim 7 or 8.